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The empirical law of effect is criticized as an incomplete step in the development of empirical laws of instrumental performance. An alternate approach to the prediction of performance is developed which follows Premack in relating instrumental performance to empirical measures of operant behavior. However, it is concluded that instrumental performance is not determined by a probability differential in operant baseline between the instrumental and contingent responses, but by the condition of response deprivation. This condition depends on the terms of the schedule as well as operant baseline measures. The response deprivation condition occurs in a contingency if, in performing the instrumental response at operant baseline, the subject would perform less than his operant baseline of the contingent response. Instrumental performance appears directly related to the amount of response deprivation. Response selection and the application of the response deprivation approach are discussed.

Associative and behavior systems accounts of Pavlovian conditioning have different emphases. The traditional associative account has focused on the role of the unconditional stimulus (US) in strengthening stimulus associations according to a set of general laws. The behavior systems account has focused on the relation of conditional responding to the preorganized perceptual, motor, and motivational organization engaged by the US. Knowledge of a behavior system enables successful prediction of the form and ease of conditioning as a function of the type of conditional stimulus (CS), US, and the CS-US relation. At the same time, Pavlovian manipulations act as a window on how a behavior system works. Both associative and behavior systems accounts can be criticized as incomplete and idiosyncratic. A comprehensive account of Pavlovian conditioning could profit from their integration. 405Laboratory-associationist and adaptive-evolutionary accounts of Pavlovian conditioning differ markedly in their focus. The former has emphasized the association between the conditional stimulus (CS) and the unconditional stimulus (US), and the role of the US in strengthening it (e.g., Hearst, 1988;Kimble, 1961;Mackintosh, 1974;Pavlov, 1927). Conditioning procedures have been refined and standardized to isolate the study of associations from the influence of instincts, nonassociative changes, and response-contingent reward (Hilgard & Marquis, 1940;Kimble, 1961). More recent models have expanded the types ofassociation and the role ofcontext, multiple CSs, the CS-US contingency, and stimulus representations in determining behavior (e.g., Miller & Matzel, 1988;Rescorla & Holland, 1982). However, the focus has remained on associations among stimuli and the simple causal role of the US. Within this approach, behavior has been treated primarily as an index of the strength of associations.In contrast, adaptive-evolutionary accounts of Pavlovian conditioning have emphasized behavior, especially the relation of the conditional response to the form and orientation of naturally occurring functional behavior and relevant underlying structure and processes (e.g., Davey, 1989;Fanselow & Lester, 1988;Gardner & Gardner, 1988;Holland, 1984;Hollis, 1982Hollis, , 1990Konorski, 1967;Rozin & Schull, 1988;Timberlake, 1983b;Timberlake & Lucas, 1989; Timberlake & Silva, in press). In this approach, establishing the perceptual-motor organiCompletion of this manuscript was facilitated by NIMH Grant 37892 and NSF Grant IBN 91 21647. The manuscript is based on a symposium presentation at the meetings of the American Psychological Association, Toronto, 1993. I am indebted to Cynthia Langley, Fran Silva, and Kathleen Silva for their comments. Please address correspondence to W. Timberlake, Department of Psychology, Indiana University, Bloomington, zation and motivational processes underlying behavior is a critical step in understanding conditioning. Presentation of the US is viewed as engaging and constraining preorganized mechanisms underlying behavior, rather tha...

This research examined three explanations for the "superstitious" behavior of pigeons under frequent fixed-time delivery of food: accidental response-reward contingency, stimulus substitution, and elicited species-typical appetitive behavior. The behavior observed in these studies consisted of occasional postfood locomotion away from the food hopper, and a predominant pattern of activity directed toward the hopper wall (wall-directed behavior), including approaching, stepping side to side, scratching with the feet, bumping with the breast, pendulum movements of the extended neck, and head bobbing, though not pecking. The consistency of these behavior patterns argued against explanation by accidental response contingencies, and the complexity of behavior was incompatible with the classic stimulus-substitution account. These studies also showed that: (1) response contingencies and prior stimulus experience can modify wall-directed behavior, but within definable limits; (2) pecking sometimes can be obtained in birds of specific strains, and by providing extended training; (3) placing the hopper in the floor at the center of a large chamber replaces wall-directed behavior with circling in a manner that resembles ground foraging for food. We conclude that superstitious behavior under periodic delivery of food probably develops from components of species-typical patterns of appetitive behavior related to feeding. These patterns are elicited by a combination of frequent food presentations and the supporting stimuli present in the environment.Key words: superstitious behavior, appetitive behavior, behavior systems, stimulus substitution, fixed-time schedules, wall-directed behavior, pecking, pigeons When pigeons receive food at frequent fixed times independent of their behavior, they rapidly develop a set of relatively stereotyped responses. These responses are typically described as "superstitious" because they emerge in the absence of actual environmental contingencies, presumably like superstitious behavior in humans (Skinner, 1948). The point of the present studies was to explore the form and causation of such behavior in pigeons. We will use the term superstitious (without quotes) to refer to behavior that emerges under a response-independent schedule, but without presumption as to its causation.The two predominant explanations of superstitious behavior in pigeons are the acci-

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